The overall goal of this project is to investigate the influence of precapillary network architecture and hemodynamics on the rate of oxygen delivery to the capillaries and tissue of striated muscles at rest and during graded contractions. Experimental and theoretical work will be carried out in parallel and the results combined to yield a detailed description of tissue oxygenation from precapillary vessels in steady and transient states. Experiments will be performed on the hamster cheek pouch retractor muscle, a muscle with a mixed fiber type composition, and the hamster sartorius muscle, a glycolytic muscle. Measurements of hemodynamic characteristics (red blood cell (RBC) flux, RBC velocity, and hemoglobin concentration), geometric characteristics (diameter, branch length and branching pattern), hemoglobin oxygen saturation (SO2) and PO2 distribution will be made in all segments of vascular pathways composed of several contiguous vessels of different branching orders to evaluate both red cell and oxygen flow balance. Measurements of the arteriolar longitudinal gradient in oxygen saturation will be made in resting hamster retractor and sartorius muscles subjected to a number of experimental perturbations including the topical application of vasoactive agents, alteration of inspired O2 and alteration of systemic hematocrit. These data will be combined with a network model of oxygen transport to yield a quantitative description of oxygen distribution in arteriolar networks. The information obtained on the resting retractor and sartorius muscles will be compared to determine if any differences in oxygen transport exist between the two muscles and if these differences can be explained on the basis of their differing fiber type compositions. In addition, the results from both muscles at rest will be compared with those obtained during and after direct electrical stimulation of the muscles. Measurements will also be made to assess the transport of oxygen at the whole muscle level. We will test the consistency between the microcirculatory and whole muscle oxygen transport measurements, an analysis which will be aided by comparison of predictions of the network model and a compartmental model formulated to describe oxygen transport at the whole muscle level.